1. Field of the Invention
The present invention relates to a semiconductor device. More particularly, the invention relates to a semiconductor device intended to realize high-speed low-power-consuming operation and to assure noise immunity by applying a voltage lower than a source voltage of a semiconductor chip to an output circuit.
2. Description of the Background Art
FIG. 13 is a schematic block diagram of a conventional semiconductor chip. In FIG. 13, a semiconductor chip 1 has therein a semiconductor circuit 11 such as a semiconductor memory or semiconductor logic and an output circuit 12. An output control signal is supplied from semiconductor circuit 11 to output circuit 12. In such a semiconductor chip 1, in order to avoid an influence of noise caused in association with an output operation of output circuit 12, in many cases, besides a power terminal to which a source voltage VDD of semiconductor chip 1 is supplied, a power terminal to which a source voltage VDDQ dedicated to output circuit 12 is provided.
When the processing speed of the semiconductor device is increased to address a demand of higher processing speed of recent years, the number of switching times between the xe2x80x9cHxe2x80x9d level and the xe2x80x9cLxe2x80x9d level increases. Consequently, power consumption increases from the relation of a voltage changedxc3x97the number of changes. To reduce power consumption, the amplitude of an output signal of output circuit 12 has to be decreased. For this purpose, as the source voltage of output circuit 12, a source voltage different from and lower than that of semiconductor circuit 11 such as a memory circuit or logic circuit has to be separately supplied from a power terminal.
However, even when a power terminal dedicated to the output circuit is provided, at the time of mounting the device onto a system, due to limitation on the number of power source layers of a mounting substrate and the like, particularly in a semiconductor memory, the power terminal is often connected to the same power source.
It is difficult to apply a voltage different from and lower than a source voltage of semiconductor chip 1 body to the power terminal dedicated to the output circuit in order to decrease the output amplitude also due to the limitation on the number of layers of a mounting substrate.
It is therefore an object of the invention to provide a semiconductor device capable of performing high-speed operation and outputting an output signal of a small amplitude without providing a power terminal for an output circuit.
The invention provides, briefly, a semiconductor device including an output circuit, having: a semiconductor circuit for supplying an output control signal to the output circuit; a power terminal to which a source voltage to be applied to the semiconductor circuit is supplied from the outside; and a power circuit for dividing an output voltage obtained by decreasing the source voltage to be supplied to the power terminal, setting the output voltage to a predetermined source potential lower than the source voltage supplied from the outside by controlling on-state resistance of a transistor for control by using a potential difference between the voltage obtained by the dividing operation and the output voltage, and supplying the predetermined source potential to the output circuit.
Therefore, according to the invention, without adding an external power terminal dedicated to the output circuit, power source noise caused in association with the operation of the output circuit can be absorbed by the power circuit, and the small-amplitude and high-speed interface can be realized.
The power circuit includes a switching transistor for supplying the predetermined source potential lower than the source voltage to the output circuit in accordance with an active signal supplied from the semiconductor circuit.
The invention also provides a semiconductor device including an output circuit, having: a semiconductor circuit for supplying an output control signal to the output circuit; a power terminal to which a source voltage to be applied to the semiconductor circuit and the output circuit is supplied from the outside; a ground terminal connected to an external ground potential; and a power circuit for generating a divided voltage on the basis of an output ground potential higher than the external ground potential, setting the output ground potential to a predetermined ground potential higher than the external ground potential by controlling on-resistance of a transistor for control by using a potential difference between the divided voltage and the output ground potential.
The power circuit includes a switching transistor for supplying the predetermined ground potential higher than the external ground potential to the output circuit in accordance with an active signal supplied from the semiconductor circuit.
Further, there is also provided a semiconductor device including an output circuit, having: a semiconductor circuit for supplying an output control signal to the output circuit; a power terminal to which a source voltage to be applied to the semiconductor circuit is supplied from the outside; and a power circuit including a comparing circuit for comparing an output potential to be applied to the output circuit with a predetermined reference potential, and a drive transistor for controlling the output potential to be a predetermined potential lower than the source voltage applied to the power terminal in accordance with a comparison output of the comparing circuit.
The power circuit may include a switching transistor for supplying the predetermined source potential lower than the source voltage to the output circuit in accordance with an active signal supplied from the semiconductor circuit.
Further, there is also provided a semiconductor device including an output circuit, having: a semiconductor circuit for supplying an output control signal to the output circuit; a power terminal to which a source voltage to be applied to the semiconductor circuit and the output circuit is supplied from the outside; a ground terminal connected to an external ground potential; and a power circuit including a comparing circuit for comparing an output ground potential to be applied to the output circuit with a predetermined reference potential, and a drive transistor for controlling the output ground potential to be a predetermined potential higher than a ground potential of the ground terminal in accordance with a comparison output of the comparing circuit.
The power circuit may include a switching transistor for supplying a predetermined ground potential higher than the ground potential of the ground terminal to the output circuit in accordance with an active signal supplied from the semiconductor circuit.
Further, a plurality of the output circuits may be provided, and the drive transistor of the power circuit is provided in correspondence with each of the output circuits.
Further, the comparison output is supplied to an input electrode of the drive transistor, the source voltage is applied to a first electrode of the drive transistor, and the output voltage is output from a second electrode of the drive transistor and applied to the output circuit, and the semiconductor device further includes: a feedback capacitor connected between the input electrode and the second electrode of the drive transistor; a first resistor connected between the input electrode of the drive transistor and the comparison output; and a second resistor connected between the second electrode of the drive transistor and a comparison input of the comparing circuit.
As the reference potential, a reference potential for an input signal may be used.
Further, a voltage dividing resistor for dividing a signal to be supplied to a comparison input of the comparing circuit via the second resistor is provided.
Further, a plurality of semiconductor chips each including the semiconductor circuit and the output circuit are arranged, and the power circuit is provided commonly for the plurality of semiconductor chips.